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Reducing pipe size on hot water radiators

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MikeG
MikeG Posts: 173
in THE MAIN WALL

My son is reinstalling 2 cast iron radiators on a hot water system. They were removed for remodeling. Previous owners in the 80s removed all but 3 and put in finned baseboard. The 2 rads are on a west wall, good location. The original piping was convoluted. The rads are 38"L x 19"H x 7"W, 22 sections. In the crawl space there are Taco monoflow tees. The original iron pipe was 3/4". Can I use 1/2" Pex-Al. I know it's rated high enough for the Temps he is running. It will make life a lot easier getting them back in service. They were capped of fo a couple years. Just looking for ideas, options etc. I have the pex, fittings and tools. Thanks. Mike

Comments

  • pecmsg
    pecmsg Posts: 7,634

    if your running 1/2” why not just run 3/4”?

  • Steamhead
    Steamhead Posts: 19,007
    https://forum.heatinghelp.com/discussion/comment/1905536#Comment_1905536

    Agreed. Especially with Monoflo tees- ISTR Taco called them "Taco-One Venturi Tees". The reduced pipe size will create too much resistance and water won't flow through the rads like it should. Don't reduce the pipe.

    Co-Founder, All Steamed Up, Inc.

    Semi-retired

    Baltimore, MD, USA

  • MikeG
    MikeG Posts: 173

    The short answer is I have a lot of 1/2" Pex-Al. I didnt want to get a bunch of 3/4 " if I didn't have to. Each take off is less than 2 feet. It's easier to make a sweep into the radiator union ells over trying to put iron pipe back. These two radiators set about 6 feet apart under windows. I'll have to see what size the main pipe is. The third radiator is on the same main pipe in a different room and was 1/2". That one we put back. All the finned baseboard comes off the monoflow tees when they removed the original radiators. I'll see what he wants to do.

  • PC7060
    PC7060 Posts: 1,980
    edited October 5

    Buy oxygen barrier three-quarter inch PEX. It’s not that expensive and there’s no need for P – AL – P.

    if you want to use the half inch lines, do dedicated runs to each radiator

  • mattmia2
    mattmia2 Posts: 18,399

    you can get copper to get it pointed in the right direction then use pex-al-pex between them.

  • EBEBRATT-Ed
    EBEBRATT-Ed Posts: 21,329

    Just use copper or 3/4" pex. Without doing all kinds of calculations that won't tell you anything because we can't see the entire system if you choke it with 1/2" you may have problems. Since it was 3/4" you probably won't.

    Does this mean the 1/2" will not work? maybe maybe not.

    If I had to guess the 1/2" will work those rads are not large. But its just a guess.

  • mattmia2
    mattmia2 Posts: 18,399

    because diverter tees divide the flow between the emitter and the main, reducing the size to the emitter could not only make that emitter not heat well but it could break the whole system by reducing the flow in the whole system

    PC7060

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